1. Field of the Invention
The present invention relates to a catalyst composition for hydrogenating olefinically unsaturated polymers, and, more particularly, to a catalyst composition having a high hydrogenation activity and useful for hydrogenating olefinically unsaturated polymers for providing the olefinically unsaturated polymers with excellent characteristics as superior weatherability, good heat resistance, superb oxidation resistance, and the like.
2. Description of the Background Art
Olefinically unsaturated polymers typified by conjugated diene polymers are widely used in industries as elastomers and the like.
The olefinically unsaturated bonds in these polymers are advantageously used in vulcanization and the like. However, they are causes for impairing weatherability, heat resistance, or the like of the polymers, imposing limitations to their application.
The poor weatherability, heat resistance, and the like can be remarkably improved by saturating the olefinically unsaturated bonds in the polymer chains by hydrogenating the polymers.
For hydrogenating polymers containing the olefinically unsaturated bonds, there are known (1) a process using an unhomogeneous catalyst composition in which a metal such as nickel, platinum, palladium, or the like is supported by a carrier such as carbon, silica, alumina, or the like, and (2) a process using a homogeneous catalyst composition prepared by reacting an organometal compound, e.g., an organic compound of metals such as nickel, cobalt, titanium, or the like, and a reducing compound, such as organic aluminum compound, organic magnesium compound, organic lithium compound, or the like, in a solvent.
The unhomogeneous catalyst supported by a carrier used in the above process (1) generally has a lower activity than the homogenous catalyst composition and thus requires more severe conditions, in terms of temperature, pressure, and the like, for effecting the hydrogenation reaction. A hydrogenation reaction proceeds through the contact of the feed materials and the catalyst. However, in the hydrogenation of polymers, the polymers are more difficult to come contact with the catalyst than lower molecular weight hydrogenation feed materials due to their high viscosity in the reaction system, steric hindrance of the polymers, and the like. Effective hydrogenation of polymers, therefore, requires a large amount of catalysts, involving a high production cost, and demands high temperature and pressure in the hydrogenation reaction, which may not only decompose the polymers or cause gelation, but also increase energy consumption. Furthermore, if the feed polymer is a copolymer of a conjugated diene and a vinyl-substituted hydrocarbon, it is difficult to selectively hydrogenating the unsaturated bonds in conjugated diene units, since, in general, aromatic rings are also hydrogenated at the same time.
In the above process (2) in which a homogeneous catalyst is used the hydrogenation reaction generally proceeds in a uniform system, wherein the catalyst is more active than in the unhomogeneous supported catalyst. Thus, the process can be operated with a smaller amount of catalyst and under a lower temperature and pressure.
If appropriate hydrogenation reaction conditions are adopted, it is possible to selectively hydrogenate the unsaturated double bonds in conjugated diene units of a copolymer of a conjugated diene and a vinyl-substituted hydrocarbon. A problem with the homogeneous catalyst composition is its poor reproducibility due to a significant variation in the hydrogenation activity depending on the reducing conditions of the catalyst composition, making it difficult to constantly produce polymers with a high degree of hydrogenation. Furthermore, the homogeneous catalyst composition loses its hydrogenation activity by impurities in the reaction system, since its components are apt to be inactivated by the impurities. This is another cause of the poor reproducibility of the homogeneous catalyst composition. Inability of constantly producing highly hydrogenated polymers with good reproducibility is a great stumbling block for the industrial application of the hydrogenation reaction using the homogeneous catalyst composition for the promotion of weatherability and heat resistance of polymers.
Furthermore, the rate of hydrogenation reactions using conventional homogeneous catalyst in the hydrogenation of polymers is not sufficiently high. In addition, the hydrogenation reaction rate decreases depending on the reducing conditions of the catalyst or due to impurities existing in the reaction system. Thus, there have been problems in hydrogenating polymers in an industrial scale by using homogeneous catalyst.
There is therefore a strong desire for the development of a high activity hydrogenation catalyst composition which is not affected by impurities in the reaction system, while producing highly hydrogenated polymers at a high rate and in a stable manner, without regard to the conditions under which it is prepared.
A hydrogenation reaction using a bis(cyclopentadienyl) transition metal compound as a catalyst component is known in the art, e.g., M. F. Sloan, et al., J. Am. Chem. Soc., 85, 4014-4018 (1965); Y. Tajima, et al., J. Org. Chem., 33, 1689-1690 (1968); Japanese Patent Laid-open (ko-kai) Nos. 133203/1984, 28507/1986, etc.
No technology heretofore known in the art, however, could solve the above-mentioned problems. There have been no publications disclosing or suggesting a solution to the problems.